1. Field of the Invention
Embodiments of the invention generally relate to conductive and semi-conductive materials and processes for forming such materials, and more particular to doped transparent conducting oxide (TCO) materials and deposition processes for forming such doped TCO materials.
2. Description of the Related Art
Multicomponent TCO complex oxides with multications have been recently developed to meet the electronic, optical, and chemical requirements for applications in the display, solar cell, and lighting industries. Carrier generation in multicomponent TCOs via metal dopants and oxygen deficiency currently are difficult to implement and controlled, however, because of the complex nature of the oxide.
From the early 1990s, multicomponent TCOs, also called multinary TCOs, have been explored and developed to meet specific electronic, optical, and chemical requirements for applications in the display, solar cell, and lighting industries. Multicomponent TCOs are complex oxides containing two or more types of cations whose concentrations often far exceed the doping levels for conventional TCOs. Depending on the materials and compositions, some multicomponent TCOs are crystalline or polycrystalline while others are amorphous. A few multicomponent TCOs also have a layered structure. To date, the majority of multicomponent TCOs are derived from the oxides such as In2O3, SnO2, ZnO, CdO, and Ga2O3.
Although many n-type multicomponent TCOs have surprisingly high carrier mobility, carrier generation has been challenging because targeted doping via aliovalent substitution is hampered by the possibility of same-valence substitution or anti-site defects which can neutralize the donors. Clustering and second phase formation can further reduce the effectiveness of the dopant. Oxygen vacancies, therefore, become a primary means to generate carriers for multicomponent TCOs. However, oxygen-deficient multicomponent TCOs can be difficult to produce in a controlled manner and can be environmentally unstable.
Existing methods for enhancing TCO materials or thin films and improving the material performance currently require expensive and energy intensive vacuum processing equipment (e.g., sputtering, low pressure plasma, PE-MOCVD), slow batch processing methods (vacuum methods, annealing in hydrogen gas mixtures) or are poorly reproducible and hazardous (in-line annealing in overpressure of gas mixtures). Several TCOs have been chemically doped during the initial growth of the TCO thin film. The decomposition of the toxic, corrosive, or explosive chemical precursor dopant source typically provides a poor level of activation of the dopant and TCO and also forms a dangerous working environment. All of the aforementioned methods increases the cost of manufacturing and reduces throughput.
Therefore, there is a need for doped TCO materials with improved conductivity and mobility of carriers, improved transparency in the visible and near-infrared (NIR) spectra, and processes for forming such TCO materials at a reduced cost of manufacturing and increased throughput.